The present invention relates generally to high-speed communications and, more particularly, to continuous low-frequency error cancellation in a high-speed differential amplifier.
Technological advances drive an ever increasing need for high capacity communications. To provide these capacities, designers strive for ever higher frequency transmissions. However, as frequencies increase, devices require more sophisticated and precise signal detection capabilities. Moreover, when distances are increased between communicating devices, a receiving device must account for low-level signals due to attenuation and increased distortion in transmitted signals.
In accordance with the present invention, techniques for continuous low-frequency error cancellation in a high-speed differential amplifier are provided. According to particular embodiments, these techniques enable the processing of high-frequency, frequency low-level signals to remove low-frequency errors.
According to a particular embodiment, a signal processing module includes multiple channel amplifiers, a low-pass filter, and an error amplifier. Each channel amplifier includes two signal inputs, two signal outputs, a supply voltage input, and a bias voltage input. The channel amplifiers form a series and each operate by receiving an input signal at the signal inputs, amplifying the input signal, and providing the amplified signal at the signal outputs. The low-pass filter receives the output signal from one of the channel amplifiers and provides filtered output to an error amplifier. During operation, the low-pass filter suppresses high-frequency components of the output signal to generate the filtered output. The error amplifier includes two signal inputs, two signal outputs, a supply voltage input, and a bias voltage input. The error amplifier receives the filtered output from the low-pass filter and provides an error cancellation signal from the signal outputs as feedback to the series of channel amplifiers.
Embodiments of the invention provide various technical advantages. These techniques help remove low-frequency errors, such as direct current (DC) offsets, from received signals and the DC offsets in the amplifier stages due to inherent device mismatches. Particular embodiments enable processing of very high-speed signals received with low-signal strength.
These techniques may further enable operation in accordance with various communication standards, while increasing the distances possible between communicating devices. For example, particular embodiments enable operation in accordance with XAUI standards, yet permit distances between devices to be measured in meters rather than centimeters.
Moreover, various embodiments achieve high-speed differential amplification with continuous low-frequency error cancellation using a single chip solution. For example, particular embodiments may be implemented using a single complementary metal oxide semiconductor (CMOS) device.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages.